The present invention relates to manifolds for supplying reaction gases to a fuel cell made up of a stack of unitary cells, and for removing the reaction gases therefrom. More particularly, the invention relates to the structure of such manifolds wherein connecting parts of electrolyte and cooling solution piping may be accommodated.
In a conventional fuel cell stack made up of multiple individual cells, each cell comprises a fuel pole and an oxidizing agent pole with an electrolyte layer held between these poles, rib-shaped fuel gas chambers supply fuel gas to the fuel pole, and oxidizing gas chambers supply oxidizing gas to the oxidizing agent pole and exhaust the gases from the cell. The fuel gas chambers and the oxidizing gas chambers are usually positioned so that the former chambers are perpendicular to the latter chambers, and the manifolds for supplying and removing the reaction gases cover the four side walls of the fuel cell stacks.
Manifolds are used in such cells to accommodate connecting parts of electrolyte pipes for supplying or circulating electrolyte to the electrolyte layers. They are further used to connect parts of pipes carrying cooling solutions to and from cooling boards that are interposed between individual cells at certain intervals in the stack. Such cooling solution maintains the temperature of the cell suitably for the generation of electric power. The manifolds are also used as a space for the pipe connections.
FIG. 6 is a sectional view of a conventional fuel cell stack taken across the vertical axis of the stack and shows the manifolds 2, 3, 4 and 5. FIG. 7 is an enlarged sectional view showing essential components of one of the manifolds of FIG. 6. In these figures, fuel gas supplying and removing manifolds 2 and 3 are provided on a pair of opposite side walls of fuel cell stack 1, and oxidizing gas supplying and removing manifolds 4 and 5 are provided for the remaining pair of opposed side walls. Fuel gas supplying manifolds 2 and 3 include, respectively, fuel gas supplying inlet 2A and fuel gas removing outlet 3A, each connected to a fuel supplying and removing system, to circulate a fuel gas (for example, H.sub.2) in the fuel gas chambers. Similarly, the oxidizing gas supplying and removing manifolds include respectively an oxidizing gas supplying inlet 4A and an oxidizing gas removing outlet 5A, connected to an oxidizing gas supplying and removing system, to circulate an oxidizing gas (for example, O.sub.2) in the oxidizing gas chambers. The result of the circulation of these gases is the generation of electric power from the fuel cell.
Each manifold described above includes a manifold cover 8, comprising a rectangular frame 6 and a rectangular cover plate 7, along with sealing means 9 interposed between the wall of fuel cell stack 1 and frame 6. As shown in FIG. 7, an O-ring 6B is inserted in a groove formed in the frame 6, whereby frame 6 and cover plate 7 are detachably joined together with screws and are airtight.
Sealing means 9 for such a manifold have previously been proposed. As shown in FIG. 7, these comprise a seal layer 10 covering the periphery of the side wall of fuel cell stack 1; a groove 6C formed in the end of frame 6 opposite seal layer 10; and seal spacer 11, which may have an H-shaped section as shown in FIG. 7, interposed between seal layer 10 and groove 6C. Seal spacer 11 is made from a material having a coefficient of thermal expansion between that of fuel cell stack 1 and that of manifold cover 8. O-rings 12A and 12B are inserted between seal spacer 11 and seal layer 10, and between seal spacer 11 and frame 6, to seal the interfaces of these components. Seal spacer 11 releases the positional shift of fuel cell stack 1 relative to manifold cover 8 caused by the variation of the temperature of fuel cell stack 1 between room temperature and operating temperature (approximately 200.degree. C.), thus preventing any loss of the seal that may be caused by the positional shift, and any damage to the packing members.
Fuel gas supplying and removing manifolds 2 and 3 accommodate an electrolyte supplying and removing pipe 22, and connecting pipes 23 connecting to pipe 22 and communicating with the unitary fuel cells. A penetrating portion 25 of pipe 22 passes through frame 6 of the manifold with an airtight interface.
In oxidizing gas supplying and removing manifolds 4 and 5, cooling solution charging and discharging pipe 19, connecting pipe 20, cooling solution manifolds 21, and a plurality of cooling pipes penetrating cooling boards in fuel cell stack 1 are accommodated such that they are suitably connected to one another, as known in the art. A penetrating portion 24 of a pipe for supplying cooling solution to the cooling solution charging and discharging pipe 19 passes through frame 6 of manifold cover 8 with an airtight seal.
In such a conventional fuel cell, the manifolds are used to accommodate the reaction gases, electrolyte and cooling solution charging and discharging pipes, and to provide a space for joining the supplying and removing pipes to the connecting pipes and for allowing the penetrating portions of the pipes and the manifold frame to interconnect, as just described. The interconnection of the penetrating portions must be carried out with frame 6 secured to fuel cell stack 1. Therefore, cover plate 7 is removed from frame 6 when this work is carried out.
These conventional fuel cell manifolds suffer from several problems. First, in order to accommodate the connecting parts of the piping, and especially the intricate electrolyte and cooling solution piping, the frame is unavoidably deep. The work efficiency of the manifold is lowered as a result. Moreover, since the manifold cover is divided into two parts, the number of sealing parts is necessarily increased as much, raising the possibility of impaired sealing performance.
In order to maintain sealing performance in these conventional cells it is necessary to increase the rigidity of manifold cover 8 as the manifold increases in size, and to provide a mechanically strong flange 6A on frame 6 so that frame 6 and cover plate 7 are sufficiently sealed. This method also undesirably increases the weight and manufacturing cost of manifold cover 8.